The invention relates generally to semiconductor device and integrated circuit fabrication and, in particular, to device structures and fabrication methods for a bipolar junction transistor.
A bipolar junction transistor is a three-terminal electronic device that includes an emitter, a collector, and an intrinsic base arranged between the emitter and collector. In a PNP bipolar junction transistor, the emitter and collector are composed of p-type semiconductor material, and the intrinsic base is composed of n-type semiconductor material. In an NPN bipolar junction transistor, the emitter and collector are composed of n-type semiconductor material, and the intrinsic base is composed of p-type semiconductor material. In operation, the base-emitter junction is forward biased, the base-collector junction is reverse biased, and the collector-emitter current may be controlled with the base-emitter voltage.
A heterojunction bipolar transistor is a variant of a bipolar junction transistor in which the semiconductor materials have different energy bandgaps, which creates heterojunctions. For example, the collector and/or emitter of a heterojunction bipolar transistor may be constituted by silicon, and the intrinsic base of a heterojunction bipolar transistor may be constituted by a silicon germanium (SiGe) alloy, which is characterized by a narrower band gap than silicon.
Conventional fabrication processes for a bipolar junction transistor may include multiple selective epitaxial growth operations to form the collector, intrinsic base, and emitter, as well as an extrinsic base used to contact the intrinsic base. The multiple selective epitaxial growth operations tend to elevate the manufacturing cost and lengthen the manufacturing process.
Improved structures and fabrication methods for a bipolar junction transistor are needed.